The need for portable, tunable lasers in the mid-infrared (mid-IR) is compelling. This eye-safe spectral region offers high atmospheric transmission essential to applications such as remote sensing and space-based terrestrial imaging and communications. Quantum cascade lasers (QCLs) have emerged as promising mid-IR sources and have even been integrated with photonic crystal resonator structures. However, QCLs typically operate from 4-10 μm, become multi-mode at high powers, and have thermal management challenges. Optically pumped gas lasers, in which a narrow-band pump laser is resonant with the gas-phase medium, can be pumped in the near-infrared to produce mid-IR emissions, but remain bulky and cumbersome.
Hollow core photonic fibers (HC-PCF) have gained wide attention due to their ability to guide in the hollow core with low attenuation over very great distances. Many nonlinear optical phenomena, including the demonstration of a Raman laser, have been observed in gas filled photonic crystal fibers. Raman lasers have been disclosed that rely on the Raman shift in the gas to shift the wavelength of a laser pulse. Such Raman lasers have many applications including a widely tunable output. However, these lasers also have certain limitations. For example, these lasers do not lend themselves to coherence conversion; that is, one cannot readily pump this laser with multiple incoherent sources and still achieve increased coherent output.